Composition for addition to cast iron or steel



Patented Jan. 8, 1,952

COIHPO SITION FOR- ADDITION TO CAST IRON OR- STEEL Jerome Strauss, NewYork, N. Y., and Daniel Leonard Edlund, Bethel, Pa., assiznors toVanadium Corporation of America, New York, N. Y., a corporation ofDelaware No Drawing. Application September 7, 1950, Serial No. 183,662

Claims. 1

This invention relates. to' a novel composition of matter for thecontrol and improvement of the physical properties of cast iron and forother uses, such as the treatment of steel in the molten state.

Cast iron is a generic term which includes gray irons, white cast irons,chilled cast irons and malleable irons. metals depend in part uponchemical factors (principallythe percentages of carbon and silicon) andin part upon physical factors, both as influenced by conditions relatedto the manufacturing methods. This is so because cast iron isessentially the product of a process and the influence of the processdetails are observed in the qualities of the product. Alloying isemployed to alter the properties of some cast irons;

also some iron castings both alloyed and not :alloyed are subjected tothermal treatments to produce desired results in castings for specificuses. The physical structure (i. e. the nature and distribution of themicro-constituents), and consequently the properties of the metal areThe properties of these' influenced not only by these several factorsbut tion range.

The cast iron which is most used commercially for constructionapplications, however, is gray iron, but this term actually covers awide range of compositions with corresponding widely varying properties.The composition of gray iron is usually confined within the limits .50to 2.75% silicon and 2.70 to 3.60% total carbon. Within this range ofcomposition the tensile strength may vary from 15,000 to 60,000 poundsper square inch and occasionally higher.

While a part of the carbon present in gray cast iron may be in thecombined form as iron carbide, the greater amount is present inelemental form as graphite. The relative amounts of free carbon andcombined carbon, as well as the shape, size and distribution of theparticles are dependent upon the remaining chemical com-- position ofthe iron and the influences referred to above, namely, maximumtemperature in the liquid state, rate of cooling during and aftersolidification, and types of heat treatment, if any, applied to asolidified casting.

Elements incidental to the production of cast iron may add or detractfrom its properties, such as strength. toughness and ductility. Sulphur,for example, is usually kept as low as possible because while itincreases the strength of the iron to some degree, it very markedlyreduces ductility. Control of sulphur depends, however, on raw materialsand process and often it cannot be held to very low values because onlyhighsulphur raw materials are available, the cost of electric furnacerefining may not be permissible and chemical treatment may not beadequate or sufilciently uniform. Phosphorusoccasionally strengthensiron but in large amountsrenders it quite brittle.

Certain elements usually considered as alloying agents have been addedto control the structure and properties of cast iron. In some cases theaddition of such alloys results in one property being improved to thedetriment of another, for example, strength may be improved but thetoughness of the iron be reduced unless some adequate form ofheat-treatment is provided to retain the toughness. In other casesimprovement in strength is accompanied by reduction in the machinabilityof the iron; in some of these cases heat-treatment, such as annealing,may restore the machinability.

It is known that magnesium added to iron which would otherwise cast grayor nearly so contributes to this iron high strength and some ductility.The ductility has in some cases been found to be increased by anannealing treatment with relatively little sacrifice in this superiorstrength.

However, serious difficulties have beset attempts to make this magnesiumpractice one that would provide with assurance successive reproductionin continuous manufacturing operations of iron articles of high strengthor high strength and good ductility. The boiling point of magnesiumbeing considerably below both the melting temperatures of those metalswith which it is preferably combined for making addition agents andbelow the temperatures at which cast iron is tapped and poured, causesextreme difficulty in controlling the overall recovery of magnesium fromraw material to the finished cast iron product.

The boiling point of magnesium is about 2030 F., which results in veryhigh losses due to vaporization of the magnesium when it is added tomolten copper and molten nickel to produce such addition agents as 20%magnesium and 80% copper, and 20% magnesium and 80% nickel. Furtherdifliculty is presented when it is attempted to introduce iron intothese compositions. Iron is a very desirable carrier metal whenmagnesium is to be introduced into iron alloys, such as gray cast ironor steel. The introduction of iron into the copper or nickel base alloysmentioned above, however, only increase the already high losses ofmagnesium during manufacture.

Since the temperature of cast'iron flowing from the cupola is normallyin the range of 2300 to 2800 F., it is obvious that additional losseswill be encountered through vaporization when magnesium alloys are addedto iron. When pure metallic magnesium is added to cast iron at suchuring temperatures, its volatilization can be e plosive in character.Magnesium continues to v porize as long as the iron remains molten andthe time element combined with the initial violent reaction results invariable losses and properties that vary beyond the limits ofsatisfactory commercial control. The use of alloy addition agents, suchas the 20% magnesium and 80% copper, and 20% magnesium and 80% nickelcompositions previously mentioned, does not satisfactorily overcomethese difliculties. For example, if the cast iron to which such alloysare added is on the high side of the above temperature range, a violentreaction will occur with high losses of magnesium through volatilizationas well as loss of metal and danger to the operators through spatteringof the molten cast iron. If, on the other hand, the temperature of theiron is low, -incomplete solution may occur, re-

' sulting in segregation and in variation in both structure andproperties throughout the product.

We have discovered in the course of extended experiments directed towardthe development of a commercially satisfactory practice for producingmagnesium-containing cast iron of predictable and reproducibleproperties that certain combinations, preferably in alloy form, ofmagnesium, silicon, manganese and iron aflord an unexpected means ofsimplification of these problems. Primarily, our discovery consists in acertain critical combination in the proportions of magnesium, silicon,manganese and iron, which substantially increases the recovery ofmagnesium in manufacture of the addition a ent as well as when thisagent is added to' molten cast iron. This combination of effects resultsin a substantial cost saving. More significant, however, is the tactthat, when using aloys of compositions within the limits of ourinvention, the desired improvements in the finished cast iron areobtainable more readily and with much greater regularity. While castiron in which substantially all of the carbon is in the form ofspheroids has been produced frequently, it has been diilicult to obtainstructurally perfect castings under production conditions with a varietyof designs, melting equipment, raw materials and other foundryconditions. An infinitely closer approach to perfection can be attainedin the use of the alloy herein described. The mechanism of the behaviorof this magnesium-silicon-manganeseiron composition within the criticalranges hereinafter set forth has not been fully explained but theresults have been obtained with such regularity both in production ofthe alloy and in its use with gray cast iron over a substantial amountof production and a large number of different foundries-that a distinctadvance in the art through its use has been established.

The ranges of composition which have produced the advantages describedare 5 to 25% magnesium, 20 to silicon, 2 to 12% manganese, the balancesubstantially all but not less than 20% or more than iron, except forcustomary impurities and minor elements, such as carbon, sulphur,phosphorus, etc., which generally do not exceed a total of 4%. Nickel isnot included among these minor elements; it is present today in some pigirons and in most iron and steel scrap and hence may be present in thesealloys up to about 2% and is not detrimental to the functioning of thealloys. In our compositions, aluminum is a detrimental element. Itshould be kept below 1% and preferably below 0.6%. Within the ranges ofcomposition already cited, we prefer to restrict the relationship of theseveral elementssothat the ratio of silicon to magnesium is not lessthan about 1:1 and not greater than about 6:1, and the ratio ofmagnesium to manganese is not less than 1 :1 and not greater han 6:1.Following are four examples of co ositions within these critical rangesand posse ing the preferred ratio of elements which were anufactured andused successfully:

The definite advantages obtained with an iron content between 20% and60% are twofold: the iron increases the specific gravity of the alloy,aiding it to penetrate the molten metal, and it raises the meltingpoint, thus slowing down the rate of solution in the molten cast iron,eil'ecting more uniform distribution throughout the mass. In addition tomelting too rapidly in the absence of iron, the cost of productionbecomes excessive if the iron is held below about 20%. If the ironcontent is permitted to exceed 60%, then the magnesium losses duringmanufacture of the alloy become excessive and very costly, and the rate'of solution of such alloys in molten cast ironis too slow and theireffectiveness is greatly impaired.

By use of alloys having compositions within the described limits,superior results have been achieved in respect to formation of nodulesof graphite in cast iron and reduction of shrinkage of cast iron, overand above what had been previously attained by the best known and mostwidely used alloy, namely, 80% nickel and 20% magnesium, together withthe development of maximum amounts of tensile strength.

The amount of alloy added to molten cast iron to be cast into gray ironcastings varies with the nature of the iron (as influenced by the rawmaterials used and the conditions of processing during melting), themaximum temperature attained by the molten iron, the temperature atwhich the addition is made, the sulphur content of the iron and perhapsother factors. In general, the addition approximates 0.12% to 0.20% ofcontained magnesium plus an amount of contained magnesium equal to 1%times the su1- compositlon, ofthe alloy being used as well as thevarious-.factorsinfluencing the character ofthe molten cast iron,as-pointed out'above, and

the method of adding the alloy to the molten iron. It is, however, agood starting. point in establishing the practice in a specific foundrywhile on a, particular melting practice so that a limited-amount ofexperimentation varying the addition upward and downward'readilyestablishes the optimum-addition required. In general, the amount ofalloy added should be suchtas to' leave-in the solidified cast. iron atotal magnesium content of'0.04 to 0.10%, preferably 005 toAnother-advantage possessed by these alloy ade ditiorl magnesium duringboth the manufacturing process and during use in the treatment of grayiron. Alloys within these ranges of composition have the peculiarcharacteristic of being dissolved sumciently easily in cast iron thatthey may be effectively used at the lowest customary pouringtemperatures which characterizemodem commercial foundry practice. On theother hand, solution is sumciently-slow that the alloy and itscomponents will be uniformly distributed throughout the melt and themagnesium will not be lost so rapidly as to prevent it from exerting itsinfluence throughout the entire mass of cast iron. No additional careand no modifica-.

tions' of prior practice are required. the. addition of the alloy toiron that would otherwise cast gray, and of low to moderate strength,being the sole requisite. The reason or reasons why these alloys melt atsuchcrictical rates so as to be usable at full effectiveness over such awide range of casting temperatures, but still melt slowly enough so thatall ingredients, and particularly the magnesium are distributeduniformly throughout the cast iron have not been clariagents isthat ofincreased recovery offled but the observations have been sufilcientlynumerous to be conclusive.

When alloys within composition ranges of the present invention are addedto cast iron, increases in strength are secured ranging from about towell over 100%, and the brittle iron becomes ductfle, with greatlyincreased resistance to shock and sudden impact. In improving themechanical properties to such high de rees the alloys covered by thisinvention regulate the microstructure of the gray iron so as to producenodular-graphite in the required amounig usuallyto the extent ofcomplete conversion of the carbon to this-form.

The presence of manganese in these alloys gives rise to two outstandingand unpredictable effects. The first is the contribution toward therecovery of magnesium in the preparation of the addition alloys. Thesecond is the part played by manganese as a component of these alloysand their effects upon the cast iron being treated. In this second casethe contribution by 6 sample 1 An outstanding, example of the effectsor; the

alloys. of: this. invention upon cast iron wasobtain'ed' when a;particularly weak iron, 1. e. low intensile strength and hardness, wastreated with: an alloycontaining: 21.25% magnesium, 34.42% silicon,4.09% manganese and the balance iron. Analysesof'the untreated andtreated compositions were as follows:

I,C, vMn Bi 5 P Mg,

Untreated 3150 0.50 2.70 0.000 0.084 .1.... MgTreated.......... 2.730.53 3.31 0.010 0.085 0.096

The tensile strength and hardness of two bars each of treated anduntreated portions of the melt, are given below:

Example 2 An addition alloy according to the invention and containing21% magnesium, 34% silicon, 4% manganese and the balance iron was addedto agray iron containing- Per cent- Total carbon 3.39

Silicon i.. 2.27

Manganese .26 Phosphorus .024 Sulphur .01

An amount of the addition alloy was used to calculate to an addition of315% magnesium based on the weight of the iron to which it was added.

The physical. properties of the treated cast iron were:

Tensile strength lbs. per sq. in.-- 62,400 Yield strength. lbs. per sq.in.-- 36,300 Elongation per cent 10 Reduction of area do- 7.1

Brinell hardness 163 Example 3 The addition alloy used in this examplecontained 24.30% magnesium, 37.79% silicon and 4.06%manganese; thebalance being iron. Various quantities of this addition alloy were addedto an electric furnace iron having the analysis:

Per cent Total carbon 3.73 Silicon 2.61 Sulphur .04 Phosphorus .15Manganese .86

In all cases where the addition of the alloy exceeded 1.50%, the ironwas practically all nodular. Tensile tests showed results ranging from61,450 to 77,100 pounds per square inch. In each case the sulphur wasreduced to practically 01%.

Methods of sampling and analysis currently in use show after theaddition of the alloys of this invention that the carbon content and thesulphur content of the untreated irons have been reduced by thetreatment. The reduction in 7' the sulphur content is no doubt due tothe combination of magnesium with at least part .of the sulphur and itsremoval as a slag or a slag forming consituent. The reason for thechange in the carbon content is not so obvious and it may be that thechange is apparent rather than real due to the diiference in the formand the distribution of the carbon and creating a necessity fordifierent methods of sampling and analysis than those commonly in use.Completely satisi'actory procedures have not yet been devised ordiscovered. I

It has heretofore been an absolute requiremen in the production of castiron having all or nearly all of its carbon in the form of spheroidsgang gm be added following the addition of the m esium alloy a secondaddition rich in silicon, such as ferrosilicon, the amount in most casesbe-v ing substantial. In the use of the alloys of this invention suchfinal addition of ferrosilicon is not a necessity and -may be dispensedwith in many cases. The amount of silicon represented by the addition ofthe alloys according to our invention is very much less than that whichwould be added according to prior art methods subsequent to theincorporation of the magnesium alloy. Even in those instances where afinal addition of silicon-rich alloy is made, the total silicon contentrepresented by this addition plus the silicon content added by means ofthe magneslum-silicon-manganese-iron alloy is distinctly less than thesilicon added as a late ferrosilicon addition according to prior artmethods. When the late i'errosilicon addition is actually employed inconjunction with the alloys of this invention, the maximum amount offerrite in the microstructure may be attained with a minimum siliconaddition, leaving not more than a very small amount of pearliticstructure in the matrix and through this means advantage in respect ofmachinability and reduction in the wear on tools used formachining willresult. Production of an iron with minimum pearlite also results inmaximum ductility of the iron composition. While fairly satisfactoryresults can be obtained in some instances in the treatment of cast ironwith compositions of matter within the ranges previously specified, notin the form of alloys but in the form of mechanical mixtures, muchbetter results are obtained by the use of these compositions in alloyform.

Alloys of this invention have also been added to molten steel forlowering the sulphur content oi the steel. For example, steels have hadtheir 8 sulphur content decreased from about .030 to about .020% by theuse of these alloys.

The invention is not limited to the preferred embodiment but may be.otherwise embodied or practiced within the scope oi. the followingclaims.

We claim: l. A composition of matter for addition to iron or steel, saidcomposition comprising about to magnesium, about 20 to 45% silicon andabout 2 to 12% manganese, the balance being substantially all iron, theiron being in an amount between about 20 and 60%.

2. An alloy for addition to iron or steel, said alloy comprising about 5to 25% magnesium, about 20 to 45% silicon and about 2 to 12% man ganese,the balance being substantially all iron, the iron being in an amountbetween about 20 and 60%. 3. A composition of matter for addition toiron or steel, said composition comprising about 5 to 25% magnesium,about 20 to 45% silicon and about 2 to 12% manganese, the ratio ofsilicon to magnesium being between about 1:1 and 6:1, the balance beingsubstantially all iron, the iron being in an amount between about 20 and1 4. A composition of matter for" addition to iron or steel, saidcomposition comprising about 5 to 25% magnesium, about 20 to 45% siliconand about 2 to 12% manganese, the ratio of magnesium to manganese beingbetween about 1:1 and 6:1, the balance being substantially all iron, theiarm being in'an'amount between about 20 and 4. 5. A composition ofmatter for addition to iron or steel, said composition comprising about5 to 25% magnesium, about 20 to 45% silicon and about 2 to 12%manganese, the ratio of silicon to magnesium being between about 1:1 and6:1, the ratio of magnesium to manganese being between about 1:1 and6:1, the balance being sub stantially all iron, the iron being in anamount between about 20 and 60%.

. JEROME STRAUSS.

DANIEL LEONARD EDLUND.

REFERENCES C ITED The following references are of record in th file ofthis patent:

1. A COMPOSTION OF MATTER FOR ADDITION TO IRON OR STEEL; SAIDCOMPOSITION COMPRISING ABOUT 5 TO 25% MAGNESIUM, ABOUT 20 TO 45% SILICONAND ABOUT 2 TO 12% MANGANESE, THE BALACNE BEING SUBSTANTIALLY ALL IRON,THE IRON BEING IN AN AMOUNT BETWEEN ABOUT 20 AND 60%.